That's the easiest way. Just use a flashlight. If I recall, there was already a thread on this topic a month or so back, so you can search back a little and check all the remarks there. If I also recall, this was the fastest method and the best way for a novice or nonprofessional.
On some of the smaller species it is difficult. I never noticed that I had two gravid M.martensii but sure enough last march I got babies all over the place. They didn't look particularly fat compared to the one male and other female I had.